Drowned creeper

This would be a mob similar to the drowned it would ether spawn naturally or if a creeper drowns. It would not be able to come out of water but would be able to swim, it would look like a moldy mushy creeper and its exclusive drop would be water gunpowder (I couldent think of any other name) If water gunpowder is combined with gravel it will create water tnt. Water tnt would be able to explode blocks if underwater but not if on land (opposite of tnt). The drowned creeper itself would be able to explode blocks if underwater but not on land ( opposite of normal creeper)